Hearing aid microphone



M L m W IF C s A w HEARING AID MICROPHQNE Filed Oct. 29, 1948 WALTER A. S CHVVAL M IN V EN TOR.

Patented Dec. 12, 1950 HEARING AID MICROPHONE Walter A. Schwalm, Oak Park, Ill., assignor to Zenith Radio Corporation, a corporation of Illinois Application October 29, 1948, Serial N 0. 57,315

This invention relates to hearing aid systems, and more particularly to such systems of the electronic type embodying a sound translator or microphone, an electronic amplifier, and a sound reproducing unit. It is a primary object of this invention to provide a system of this type in which a substantial improvement in performance is effected.

In the usual hearing aid systems, a customary practice is to support the sound translator or microphone by its back portion on a form of cushioning or sound-dampening material. External sounds impinge upon the microphone through a grille covered opening in the front of the case. Much discomfort and annoyance have been experienced by users as a result of noises produced by pieces of clothing material rubbing together in the vicinity of the microphone grille opening and by outer garments of clothing touching or rubbing the hearing aid case. The noises produced by pieces of clothing rubbing together are transmitted to the microphone by air conduction; the case noises are transmitted to the microphone by (a) conduction through the case to the grille and thence by air to the microphone, and (b) conduction through the case to the microphone mounting and thence into the microphone by virtue of the pick-up characteristics of the back side of the microphone. These noises, which are of various intensities and tones, impair intelligibility due to consequential interference with desired sounds and are of themselves of no value to the user. Therefore, a reduction or elimination of clothing-induced noises would be beneficial to users of hearing aids, and a system of affording such a reduction would be a meritorious contribution to the hearing aid art.

It is therefore an object of this invention to provide an improved hearing aid system in which is afforded a greater degree of utility than in previous systems by virtue of a novel means of reducing the introduction of extraneous noises.

It is a further. object of this invention to incorporate in a hearing aid an improved acoustical system in conjunction with the microphone thereof, thereby to exclude, to a great extent, undesired clothing-generated noises without detrimental effect on the reproduction of desired sounds.

In the use of hearing aid systems, a widespread practiceof users is to wear the case, containing the microphone, in a front pocket of an intermediate garment of outer clothing, as for example a shirt or a vest. Some degree of sound muflling occurs due to the impedance to sounds 4 Claims. (01. 179-4017) offered by the front of the pocket covering the microphone grille. If the wearer places another garment, such as a coat, over the intermediate garment, the additional layer of cloth further muflles desired sounds, usually to such an extent as to impair intelligibility.

Therefore, it is another object of this invention to incorporate in a hearing aid an improved acoustical system in conjunction with the microphone thereof, b the use of which system the transmission of desired sounds to the microphone is improved.

In some forms of hearing aid sytems, the microphone is located in a case wherein the electronic system controls are situated. These controls -of necessity must be readily accessible to the user, and for this purpose, openings in the case are provided for, control knobs. In actual usage, sounds not only impinge on the microphone through the grille openings, but a sound path to the microphone also exists through'the control knob openings. This multiplicity of paths of the microphone produces a directional efiect on incoming sounds. Thus, the user finds his hearing aid susceptible to sounds emanating from undesired directions. At the same time, cancellation of certain frequency components results, and the quality of sound reproduction is considerably impaired. Therefore, still another object of this invention is to provide an improved hearing aid system in which a multiplicity of paths of sound to the microphone is effectively eliminated.

In hearing aid systems, the microphone in use may not provide uniform response to the various tone components of impinging sounds, since emphasis in hearing aid design is often placed on space and Weight considerations, rather than on fidelity of reproduction. It is, therefore, still another object of this invention to provide an improved acoustical system for shearing aid, the use of which system affords improved fidelit of sound reproduction while making little or no addition to space and weight requirements.

The features of the present invention, which are believed to be novel are set forth with particularity in the appending claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood. however, by reference to the following descrip tion taken in connection with the accompanying drawing in which:

Fig. 1 shows a fragmentary cut-away plan view of a portion of a hearing aid unit incorporating an improved acoustical system in accordance with the present invention; and

Fig. 2 shows a partial section along the line I In accordance with this invention, sound waves pass into microphone ll solely through an opening in the top portion of the outer periphery ,of hearing aid case I0.

In Fig. 2, there is illustrated a side elevation in transverse section of the unit or Fig. ;1,inco rlporating the housing portions I4 and N3 of microphone I l, the microphone diaphragm (6, drive pin l1, translating device such as piezo electric element l8 and piezo electric element supports 19, 2B and 2|, (see Fig.1). within the hearing aid case Hi and is glued to a cir. cular mounting pad 22 of resilient material which is in turn glued to the hearing aid electronic amplifier chassis 23. In addition, the microphone is der, closed at one end, but having a structure 3| formed integrally therewith and extending radially from the top-front part of portion l4. Structure 3| contains sound funnel 25 and channel 26; the axes of which are substantially parallel to the plane of portion M of microphone H. Diaphragm I 6 is preferably a cone constructed of aluminum ,foil or other suitable material and having a peripheral rim by means of which it is supported between the adjacent rim portions of members [4 and I5.

Cavities .21 and 28 are of such dimensions as to provide the optimum frequency response characteristic commensurate with practical space phragm l6, and the stiifness and mass of piezo Microphone II is enclosed supported by a rectangular mounting pad :24, of

' of its four corners to mounting pads 19, 20 and 2| respectively, which pads are in turn glued or fastened to the inner wall of-portion l5 of microphone H; the free, fourth corner of element 18 being in direct mechanical connection with the center of diaphragm 16 by means of drive pin H. Piezo electric element i8 is thereby physically distorted in accordance with incoming sound variations and produces correspondingly variable electrical potentials at output leads 29 and 30. These varying electrical potentials are then impresed on the input terminals of a con ventional electronic amplifier (not shown) and thence to the ear piece or receiver (not shown) for conversion to amplified sound variations. It is apparent that other types of sound transducer elements; for example, a carbon button element or an electromagnetic element, may be used to perform the exact function here realized by the piezo electric element I8. It is also apparent that other cross sections, as circular for example, will properly function for funnel 25, channel 26 and aperture 32.

In the construction of microphone ll, portions I4 and [5 preferably are termed of a malleable metal, such as aluminum or brass, havinga cross section of appreciable dimensions, one-sixteenth of an inch for example, order that the microphone walls shall be opaque tov sounds impinging on the outer surfaces of microphone H. ited to the passage defined by funnel 25, channel 26 and aperture 32. Portion l5 of micro..- phone H is in the shape of a hollow cylinder. closed on one end. Portion l4 of microphone U is also in the ,shape of a hollowcylim Sound entry to the diaphragm is lirnand frequency selective effects.

electric element l8. Cavity 2'! is open to free air through aperture 32, channel 26 and funnel 25. The size of cavity 23 operates ;in conjunction with the size of aperture 32, the length and cross section of channel 26 and the slant height and cross section of funnel 25 to produce resonant therefore, empirical adjustment can be made in a manner well known to the art, whereby the resonant and frequency selective efiects operate to provide a substantially uniform frequency response characteristic for microphone H. The

following dimensions have been found suitable in one specific application of the invention and are presented by way of example only: All dimensions are in inches. a

In use, sound entry is limited to funnel 25 and channel 25 because the sound-opaque heavy outer walls of microphone ll preclude the possibility of transfer of sound or mechanical dimensional variations to diaphragm [6 by distortion of the microphone case portions l4 and i5. The sound cushioning mounting for microphone H, em bodied in the resilient mountings 22 and 24, "insulate microphone l i from vibration of the hearing aid case [0. Therefore, vibration, such as that caused by rubbing contact with clothing, is substantially precluded from transmission to the microphone diaphragm l6. Also, as sound entry is' limited solely to funnel '25, channel 26 and aperture 32, there can be no multiplicity of sound paths to the microphone diaphragm it which might exist as a result of other openings in hearing aid case it], and directional and cancelling effects are thereby averted. Further, since the sole opening to diaphragm i6 is through cavity 21, aperture 32, channel 26, and funnel 25, muriiing effects of aflpocket or outer garments of clothing, where. the aid is worn'in the users pocket, will be substantially reduced, since free air space usually will existin the vicinity of the top of hearing aid case 10, and sound entry to this free, air space will be through a relatively large area of clothing. Finally, since the dimensions of cavity 2'8, cavity '21, aperture -32,'cha:nnel 25 and funnel 25 are established for, optimum frequency response in microphone H, improved fidelity is attained over prior devices having, for example, cavity 28 only.

It is contemnlatsdnthat apiece of fe t 9r flam- In pi'actice,

nel, or other acoustic damping material be disposed within funnel 25 for the purpose of deemphasizing peaks in the frequency response characteristic of microphone ll, thereby to prevent overloading of the electronic amplifier (not shown) and to substantially eliminate resulting inter-modulation products.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from th s invention in its broader aspects, and, therefore, the aim in the appended claims is to cover such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. A hearing aid for amplifying and reproducing sound waves comprising: a case includ=- ing a front portion, a back portion and an enclosing edge portion provided with a sound-admitting aperture which is located solely in the top-peripheral portion of said case and which has a length less than that of said top portion; a microphone assembly within said case including a housing having a sound admitting aperture and including a diaphragm in spaced parallel relationship with said front case portion and in registration with said housing aperture; a closed sound directing conduit member having a pair of openings registering respectively with and extending between said apertures of said case and said housing and constituting the sole sound passage to said diaphragm; and support means for supporting said microphone assembly within said case and for substantially acoustically insulating said microphone assembly therefrom.

2. A hearing aid for amplifying and reproducing sound waves comprising: a case including a front portion, a back portion and an enclosing edge portion provided with a sound-admitting aperture which is located solely in the top-peripheral portion of said case and which has a length less than that of said top portion; a microphone assembly within said case including a housing having a sound-admitting aperture and including a diaphragm in spaced parallel relationship with said front case portion and in registration with said housing aperture; a closed funnel-shaped sound directing conduit member having a pair of openings registering respectively with and extending between said apertures of said case and said housing and constituting the sole sound passage to said diaphragm; and support means for supporting said microphone assembly within said case and for substantially acoustically insulating said microphone assembly therefrom.

3. A hearing aid for amplifying and reproducing sound waves comprising: a case including a front portion, a back portion and an enclosing edge portion provided with a sound-admitting aperture which is located solely in the top-peripheral portion of said case and which has a length less than that of said top portion; a microphone assembly including a substantially sound opaque housing having a sound-admitting aperture and including a diaphragm in spaced parallel relationship with said front case portion and in registration with said housing aperture; a closed sound directing conduit member having a pair of openings registering respectively with and extending between said apertures of said case and said housing and constituting the sole sound passage to said diaphragm; and support means for supporting said microphone assembly within said case and for substantially acoustically insulating said microphone assembly therefrom.

4. A hearing aid for amplifying and reproducing sound waves comprising: a case including a front portion, a back portion and an enclosing edge portion provided with a sound-admitting aperture which is located solely in the top-peripheral portion of said case and which has a length less than that of said top portion; a chassis supported within said case; a microphone assembly supported on said chassis and substantially acoustically insulated therefrom and from said case, including a housing having a sound-admitting aperture and including a diaphragm in spaced parallel relationship with said front case portion and in registration with said housing aperture; and a closed sound directing conduit member having a pair of openings registering respectively with and extending between said apertures of said case and said housing and constituting the sole sound passage to said diaphragm.

WALTER. A. SCHWALM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,026,231 Williams May 14, 1912 1,209,291 Hastings Dec. 19, 1916 2,304,339 Cubert Dec. 8, 1942 2,351,400 Carlisle June 13, 1944 2,358,099 Polk Sept. 12, 1944 2,417,153 Darr Mar. 11, 1947 

